Naval radar systems search space using a plurality of sequential directional beams which may be pointed in a given direction. In general, an acquisition face (volume) to be searched is defined, and the radar beam is directed so as to cover the entire search face. This type of searching is subject to time constraints, as the beam must dwell at a particular beam angle long enough for the transmitted radar signals or pulses to travel to the target and for the reflection to return to the radar.
When information becomes available from another source, such as a cooperating radar, about the possible presence of a target in a given direction or location, it may be desired to examine a volume about the nominal given direction in an attempt to acquire the target. This is referred to as a “cued” search. If the selected volume is too large, the search may time-out before completion. By contrast, if the selected volume is too small, the target might not be found.
In general, methods are known for searching a search volume about a given cued direction and with a given maximum search range. The search of a designated volume is, as noted, performed with sequentially generated radar beams. Such methods may involve acquiring the nominal track position and velocity (cue information) and time, as well as error information describing the uncertainty in the cue information. This error information may be presented together with the cue information. From the error information, the azimuth and elevation extent (the acquisition or search face) of the search volume about the cue direction is determined.
Partitioning methods may be used in an attempt to optimize the creation and search of cued acquisition volumes in such radar systems. An acquisition face describes the elevation and traverse (azimuth) extents about a central position, such that they enclose an area of estimated uncertainty. A radar beam may be described as a cone with a generating angle representing the beam width. The beam width is defined as the diameter of the beam. The intersection of a beam with the acquisition face is a circular region within which the beam energy is greater than or equal to the minimum drop-off energy. A beam forming radar may search the region by placing successive beams so as to form an overlapping pattern such that lines connecting adjacent beam centers describe a hexagonal tiling of the acquisition face. Each placed beam requires a time delay to complete its scan, consisting of the times for the beam to propagate over the selected range and back and the time to clear the emitter/receiver. The acquisition volume is time limited to a maximum search interval, i.e., for various reasons a search volume is considered valid by the radar only for a limited time, even though this time may be less than the time required to complete the search if the number of beams required is large and extended waveforms are used. Thus, methods have been sought to partition a search volume into searchable segments, one of which is sent to the radar and the remainder re-calculated for the subsequent search interval.
Methods have been described for reducing the number of radar beams required to exhaustively search an acquisition volume face during an attempt to acquire a target from a remote cue, wherein the projection of a covariance onto the traverse/elevation plane is rotated so that the principal axes of the projection align with the axes of the plane. The acquisition volume is then calculated in terms of traverse and elevation centers and extents and sent to the search radar along with the rotation angle. The search radar determines if a beam is within in the transmitted acquisition volume according to its criteria, and if it is, then the beam is rotated back through the angle of rotation to determine its final position. Such rotation methods, however, do not address partitioning. Thus, there remains a need for an improved partitioning methodology that insures that effective partitioning occurs within application constraints.